DETERMINATION OF THE BIMOLECULAR RATE-CONSTANT OF PHOTOINDUCED CHARGE SEPARATION IN THE ENERGY-GAP REGION WHERE THE REACTION IS DIFFUSION CONTROLLED - ANALYSIS OF THE TRANSIENT EFFECT IN THE COURSE OF FLUORESCENCE QUENCHING REACTION

The photoinduced intermolecular charge separation (CS) rate constant (k(CS)) at the encounter in acetonitrile solution has been evaluated for various donor-acceptor pairs by analyzing the transient effect in the fluorescence decay curves, in the energy gap gion -DELTA-G0 = 0.37-2.21 eV, where the reaction is diffusion controlled. Although the obtained k(CS) values are larger than the diffusion rate constant, they do not show the typical bell-shaped -DELTA-G0 dependence as observed in the charge recombination reaction of the geminate ion pairs produced by fluorescence quenching reaction, but show a rather flat shape.